In the field of vehicle headlights, LEDs have largely forced conventional filament lamps out of the market due to their compactness and energy efficiency.
While a filament radiates in all directions, an LED at best does so in a half space. This must be considered during the construction and arrangement of the beam shaping components of the headlight. While both reflectors and refractive light elements are as a rule used in a headlight with filament lamps, to collect the emitted light and shape it into a light bundle, a reflector is sufficient for this purpose in a headlight with LED lamps.
To avoid glare caused by the light radiated by the LED lamp directly toward oncoming traffic, it is helpful to orient the light-emitting surface in such a way that it is not visible from the viewing direction of oncoming traffic, e.g., to downwardly direct its surface normal, so that essentially downwardly directed emitted light is reflected by the reflector in a roughly horizontal, final main direction of propagation. To obtain only a slightly divergent light bundle after reflection, the LED lamp must be placed near the focus of the reflector, which makes the overall height of the headlight distinctly larger than the cross section of the light bundle radiated by it. This makes it harder to accommodate the headlight on the vehicle.